I don't think you need to worry about your blade being too fragile to open more than just mail. As long as you use your head and don't place any undue lateral stress on the tip, you can cut pretty much anything you want (so long as it's made of a material that's harder than the blade). I use a Military heavily all of the time and it has a freakishly thin tip. No problems whatsoever. Sal and co. wouldn't sell a knife that wasn't tough enough to cut reasonable things without breaking. The ones that were not designed for everyday cutting are clearly marked as such right out of the box (like the Civilian).
If you use your Yojimbo to pry and chop hard wood, then you might possibly break the tip. Otherwise, relax and don't worry about it. Your knife is a tool and is meant to be used. Cutting stuff is what it was born to do. You'll be suprised at how good it is at the job.